(1) Field of the Invention
The present invention relates to an image forming apparatus which forms images on a recording medium by causing the developer to jump thereto and in particular relates to an image forming apparatus in which a sufficient amount of toner can be secured for neighboring gates, to thereby prevent degradation of the image.
(2) Description of the Related Art
Conventionally, as a technology to produce a visual image in accordance with an image signal onto a recording medium such as paper and the like, a configuration has been known in which an image is formed directly on the recording medium whilst the passage of charged particles jumping through gates is controlled.
For example, Japanese Patent Application Laid-Open Hei 6 No. 344, 588 discloses an image forming apparatus in which charged particles are placed in an electric field so that they will jump by electric force whilst the potential being applied to the control electrode, having a number of passage holes and located in the jump path, is being varied, to thereby make the charged particles adhere to the recording medium, thus forming a visual image on the recording medium, directly.
In image forming apparatuses of this type, represented by this prior art, either the jumping or non-jumping of toner is selected by controlling the electric field formed between the gates and the toner support, so that the toner is made to reach to the paper surface as a recording medium by a strong electric field generated by the opposing electrode.
However, in a configuration in which the control electrode is spaced about 100 .mu.m for example, from the toner support, the area on the toner support from which toner has jumped is usually greater than the area of the gate provided on the control electrode. In other words, when the toner is caused to jump through a certain gate, toner jumps toward the gate from an area greater than that of the gate. Therefore, when taking into consideration a plurality of gates neighboring each other, there occur cases in which the area on the toner support opposing each gate may have an insufficiency of toner.
In this way, if a sufficient amount of toner cannot be secured for neighboring gates, dots having a predetermined diameter and a predetermined density cannot be formed, resultantly producing degradation of the image. In particular, when a monochrome solid image in which a certain density of a color is printed uniformly (hereinbelow referred to as `solid image`) needs to be formed, areas with a lower amount of toner will appear as white lines. On the other hand, when a multi-color image is taken into consideration, out of registration occurs so that it is impossible to reproduce the correct original colors.
If this problem is tried to be solved by increasing the amount of toner on the support, or by increasing the conveyed amount or the packing density of toner, it becomes more difficult to form a stable toner layer as the packing density or the conveyed amount is increased more and more because of the fact that the characteristic values of the toner cannot be controlled independently.
On the other hand, even if the voltage to be applied to the gates to cause jumping of the toner is increased or if the pulse width of the voltage to be applied is made greater toward the downstream side, this method is only effective within a markedly limited range of applications and is not practicable to a real situation, because such defects do not always occur at the specified gates.